1. Field of the Invention
The invention relates to high voltage regulated direct current power supplies generally and more particularly to such power supplies for use with pulsed loads.
2. Description of the Prior Art
In the prior art there have been many approaches to the problem of voltage regulation for electronic equipment. These prior art art approaches include series and shunt regulators, switching-type regulators and others.
Voltage regulation at very high voltages (tens of thousands of volts) is particularly difficult to accomplish economically in series or shunt circuits, because of the high voltages themselves and because of the power waste frequently associated therewith. Switching-type regulators generally speaking offer the most economical approaches and are particularly adaptable for pulse electronic equipment which operates over a relatively short duty cycle and draws little or no load current between pulses. The radio frequency power amplifiers of modern radar systems employing travelling wave tubes or similar devices, fall into that general load category.
A relatively recent device of the general character, i.e., a high voltage low-duty cycle power supply, was described in U.S. Pat. No. 4,153,871. That disclosure outlines the prior art situation in somewhat more detail, and the comments therein are applicable to the prior art situation as related to the invention herein described.
The device of U.S. Pat. No. 4,153,871 is described as a boot-strap regulator and involves power supply filter capacitor charge current sensing and integration for controlling the so-called "boot-strap" voltage applied across a small capacitor in series at the ground end of the main power supply filter capacitor. Thus, low voltage control circuitry may be employed.
The regulator described in the aforementioned U.S. Pat. No. 4,153,871, although successful, is somewhat more complex than is desirable from an economic point of view. Moreover, that prior art device operates its switching functions synchronously with the RF pulse processed by or through the apparatus which it powers, whereas it is desirable that the power supply for a traveling wave tube or the like be self synchronous in its switching operations and not dependent upon system triggering.
In a radar system employing a traveling wave tube, a high negative cathode voltage is required. In a typical implementation of the present invention, a TWT cathode voltage of 45,000 volts was required. The phase stability of the traveling wave tube is related to this cathode voltage; and in MTI systems or other signal processing systems, the repeatability and stability of the initial TWT cathode voltage at the beginning of a transmitting pulse are the important considerations, it being relatively less important that the high negative cathode voltage remain undiminished during the power pulse, provided the variation of that voltage is accurately repeatable and begins from substantially the same initial voltage.
The particular manner in which the invention provides an effective yet very economical configuration for regulating a direct current, very high voltage for the type of load described will be evident as this description proceeds.